Contact lenses are an extremely popular method of vision correction. Unlike glasses, they are all but invisible, and many versions can be worn for extended periods of time. In recent years, contact lenses have been developed that will not rotate once placed on the eye, permitting the use of contact lenses to correct astigmatism as well as myopia.
Unfortunately, although commercially available contact lenses are an excellent choice for vision correction when only one prescription is required per eye, no practical method has yet been developed for permitting a wearer to look through different portions of the contact lens to adjust the degree of vision correction, as is done with multiple-prescription glasses such as bifocals. By their nature, contact lenses are designed to center themselves on the pupil, regardless of whether the wearer moves his eyes up, down, or to the side. Commercially available contact lenses are thus ill-suited to the needs of wearers that require multiple prescriptions.
A number of patents and patent applications attempt to address this dilemma by providing for a contact lens that is thickened at the base, causing the lens to “catch” on the lower lid of the eye and thus permit the eye to translate downward, viewing through a different portion of the contact lens. Unfortunately, this approach has a number of serious drawbacks: the thickened lens can be uncomfortable, and older patients (who are more likely to need bifocals or other multiple prescription lenses) generally have eyelids that are less firm and thus less able to provide the support required to immobilize the lens and permit translation. One variation on this idea, embodied in U.S. Pat. No. 4,702,573, relies upon a thickened “base” pressing against the lower lid to cause a deformation in the lens itself, thus changing the prescription. This approach suffers from the same difficulties as other lens configurations that rely upon the lower lid of the eye, because a loss in elasticity of the lower lid will effectively change the corrective prescription of the lens.
Thus, there is a need for a contact lens that permits the eye to translate from one portion of the lens to another, to allow for viewing through different parts of the lens. The present invention permits this translation by utilizing the lower fornix of the eye (i.e., the bottom of the fold of the fornix where the bulbar conjunctiva meets the palpebral conjunctiva) to stabilize the contact lens, permitting translation of the eye to different portions of the lens. Additional advantages of the invention will be set forth in part in the description that follows, will in party be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will also be realized and attained by means of instrumentalities and combinations particularly pointed out in the appended claims.